In recent years, organic EL panels making use of electro-luminescence in organic materials have been actively developed. An organic EL panel has a plurality of pixels arranged in a matrix of rows and columns. The number of pixels varies depending on resolution. For example, resolution of Full HD is 1920×1080, and resolution of 4K2K is approximately 4000×2000. Each pixel is composed of a plurality of sub-pixels emitting light of different colors. The colors of light are typically red (R), green (G), and blue (B). Full HD is currently popular as a standard for resolution of a digital television. As a next generation standard, 4K2K having a higher resolution than Full HD has been proposed. The number of pixels of 4K2K is approximately four times the number of pixels of Full HD.
Meanwhile, display panels can have display defects referred to as an unlit dot, a dark dot, and a bright dot. The unlit dot refers to a case where a light-emitting element in a sub-pixel is constantly off. The dark dot refers to a case where a light-emitting element in a sub-pixel constantly emits dim light. The bright dot refers to a case where a light-emitting element in a sub-pixel constantly emits bright light.
It is extremely difficult to reduce the number of display defects to zero in manufacturing the display panels. Thus, a display panel having some display defects is usually shipped as a non-defective product if the number and distribution of the display defects are within an allowable range. The allowable range for the display defects is defined for example in IS013406-2.